This invention relates to a four-crawler-driven vehicle which is moved on or along a floor in a dangerous environment by remote control or automatic control for inspection and maintenance in a nuclear plant, for example.
Generally, application of remotely operated robotic crawler vehicles to a nuclear plant such as an interior of the primary containment vessel for inspection and maintenance thereof is essential from the point of reducing radiation exposure dose to operation personnel. A robotic vehicle of this type comprises a main body on which controlling or operating equipment for inspection and maintenance is mounted, crawler assemblies attached on both sides of the body, a steering mechanism attached to the body for steering the crawler wheels, a drive mechanism for driving the crawler vehicle, and a power transmission mechanism for transmitting driving power from the driving mechanism to the crawler wheels.
However, a conventional crawler vehicle generally comprises one crawler assembly at each side thereof and is moved by the rotation of these crawler assemblies, so that the vehicle has less moving freedom and can move only in limited ways.
To obviate defects of the crawler vehicle of the type described above, there has been proposed a crawler vehicle provided with four crawler assemblies, two on the respective bilateral sides, for improving the moving freedom so that the crawler vehicle can move in a greater variety of ways. This four crawler vehicle is driven and steered by causing a speed difference in the crawler assemblies on the bilateral sides of the vehicle body. However, with the four crawler vehicle of this type, it is difficult to obtain an ideal moving state during the operation thereof for the reason that slipping degrees of crawlers of the crawler assemblies on both sides may widely be different according to varying conditions of a floor on which the crawler vehicle moves.
In addition, with the crawler vehicle, it is required to have a good performance for getting over obstacles or stepping up or down stairs or steps in the nuclear primary containment vessel, for example, as well as good steering performance. Although, in order to obtain an excellent obstacle-surmounting performance or step-up or -down performance, it is generally required to increase the diameter of a crawler wheel, this increase adversely affects the stability of a vehicle and load mounting space of the vehicle body.